1. Field of the Invention
The present invention relates to cryogenic pumps and more particularly to a high pressure cryogenic fluid generator for use in cryosurgical procedures.
2. Description of the Related Art
The distribution of boiling (liquid) cryogens, such as liquid nitrogen, is problematic due to the parasitic heat load provided by a cryosurgical device's plumbing or transport circuit, which is maintained at ambient temperature. Pre-cooling the plumbing circuit, even if adequately insulated, causes two-phase flow (liquid-gas mixtures), cryogen boil-off, and choking flow due to gas expansion in the transport circuit. As a result, target temperatures at the distal end of the flow path (i.e., cryoprobe tip) are not reached for many minutes.
Some prior cryogenic systems and devices are disclosed in U.S. Pat. No. 4,345,598 to Zobac et al.; U.S. Pat. No. 4,472,946 to Zwick; U.S. Pat. No. 4,860,545 to Zwick et al.; U.S. Pat. No. 4,946,460 to Merry et al.; U.S. Pat. No. 5,254,116 to Baust et al.; U.S. Pat. No. 5,257,977 to Eshel; U.S. Pat. No. 5,334,181 to Rubinsky et al.; U.S. Pat. No. 5,400,602 to Chang et al.; U.S. Pat. No. 5,573,532 to Chang et al.; and U.S. Pat. No. 5,916,212 to Baust et al., the entire contents of each being hereby incorporated herein by reference thereto, respectively.
U.S. Pat. Nos. 7,416,548 and 7,192,426, both issued to Baust et al., and both entitled “Cryogenic System,” disclose a cryogenic system with a pump assembly using a bellows that is submersible in cryogen which provides pressure to a cryoprobe greater than 250 psi. These patents are incorporated herein by reference, in their entireties, for all purposes.
Barber-Nichols, Inc. (BNI), Arvada, Colo., manufactures a Long Shaft Cryogenic Pump that uses a long, thin-walled shaft to separate the impeller (cold end) from the motor (warm end). This shaft minimizes heat leaking from the motor and atmosphere into the cryogenic fluid. However, the Barber-Nichols pump is rather bulky and cannot generate pressures in ranges required by the present applicant, i.e. greater than 250 psi.
Near critical cryogenic fluid generators are disclosed in, for example, U.S. patent application Ser. No. 10/757,768 which issued as U.S. Pat. No. 7,410,484, on Aug. 12, 2008 entitled “CRYOTHERAPY PROBE”, filed Jan. 14, 2004 by Peter J. Littrup et al.; U.S. patent application Ser. No. 10/757,769 which issued as U.S. Pat. No. 7,083,612 on Aug. 1, 2006, entitled “CRYOTHERAPY SYSTEM”, filed Jan. 14, 2004 by Peter J. Littrup et al.; U.S. patent application Ser. No. 10/952,531 which issued as U.S. Pat. No. 7,273,479 on Sep. 25, 2007 entitled “METHODS AND SYSTEMS FOR CRYOGENIC COOLING” filed Sep. 27, 2004 by Peter J. Littrup et al.; U.S. patent application Ser. No. 11/447,356 which issued as U.S. Pat. No. 7,507,233 on Mar. 24, 2009 entitled “CRYOTHERAPY SYSTEM”, filed Aug. 6, 2006 by Peter J. Littrup et al.; U.S. Pat. Nos. 7,410,484, 7,083,612, 7,273,479 and 7,507,233 are incorporated herein by reference, in their entireties, for all purposes.